Just this last week, I took my 12 year old tortie, Kitty, to the vet. She has a good appetite but was vomiting a lot and had lost weight. Other than the vomiting, she seemed fine, and in fact still plays like a kitten. Her blood work looked great. The vet suggested an x-ray. The x-ray showed a mass in her abdomen. I was then referred to a specialist for an ultrasound. We went yesterday for that and it was determined that Kitty has a mass in her small intestine and an inflamed lymphnode adjacent to the mass. The vet expected it to be lymphoma but a needle biopsy revealed the mass to be mast cell cancer.

I have read that common signs of problems like this can be loss of appetite and weight loss. Hopefully, your kitty is not as sick as mine but the x-ray and/or ultrasound is probably worth doing if you can afford it. Of course, you may want to get thyroid checked first as ultrasounds are expensive.